Purpose: Careful selection of beam number and orientation is of critical importance for external beam treatment planning. The utilization of well-chosen non-coplanar beams could allow the generation of high-quality plans. This study is to evaluate the quality of the IMRT plans generated with the non-coplanar (NCP) beams selected with our in-house program by comparing it with coplanar (CP) IMRT and RapidArc (ARC) plans for prostate and pancreatic cancer treatments.

Methods:Ten patients with prostate and pancreas cancer treated previously were selected for this study. A set of 13 non-coplanar beams was selected with our in-house program based on the CT data of one patient and was used to generate NCP plans for the ten cases. For each case we also generated an eight-beam CP and a double-arc ARC plan. All plans were generated with the Varian Eclipse TPS. For individual cases, the same dose-volume constraints and weightings were used for all three plans.

Results:All plans provided conformal and complete converge of the PTV and led to clinically acceptable doses to the organs-at-risk. The NCP plans show the best quality in terms of PTV Dmean, Dmax and HI, while the ARC plans are best in terms of PTV Dmin and CI. For the prostate cases, the NCP plans show the best V₄₀ and V₆₀ for rectum and bladder, and best D2% for the right-femoral head, while the ARC plans show the best left-femoral head D2%. For the pancreas cases, the NCP plans show the best sparing of the left- and right-kidney as well as the spinal cord. However, the NCP plans lead to slightly worse Dmean and D1/3 to the liver than the CP plans.

Conclusion:We have shown that the non-coplanar beams selected with our program allow the generation of high-quality IMRT plans, by comparing them with the conventional IMRT and RapidArc plans.